For Louis van Gaal, there will be no trophy in his first season to justify what he says about Manchester United being back on an upward trajectory.

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Welbeck

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His team fell way short against Arsenal on Monday night and the indignities were considerable bearing in mind the identity of the player who struck the game’s decisive moment. Danny Welbeck will certainly have relished his goal given Van Gaal’s unflattering remarks about him earlier in the season, but that still told only part of the story from a night that seemed to say so much about the home side’s various shortcomings this season.

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Arsenal had been sharper and less error-strewn on a night that will also be remembered for the latest ignominy in Ángel di Maria’s short and unsatisfactory time with the club, sent off for gross stupidity as United went huffing and puffing after an equaliser. Di Maria’s first yellow card was for diving and the second followed moments later when he took umbrage with the decision and yanked at the referee Michael Oliver’s shirt. It was a moment of dim-wittedness that should embarrass the most expensive player in Britain. Radamel Falcao could not even get off the bench and United were looking desperate by the time the substitute Adnan Januzaj was booked later on for another dive.

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Arsenal, in stark contrast, won because they passed the ball more effectively and made fewer mistakes. They took the lead through Nacho Monreal after 25 minutes and, though Wayne Rooney equalised shortly afterwards, there was never a concerted spell when the home side looked like the superior team.

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This fixture might not have the dynamism of old; the rivalry is not so extreme, and Daley Blind versus Francis Coquelin feels like a display of good manners compared to the days of Roy Keane versus Patrick Vieira. But there is still a lingering edge. The two teams seemed to be suffering from nervous energy at times, miscontrolling the ball and rushing passes. More than anything, both reminded us again that their defences deserve their reputations for being accident-prone.

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The carelessness was due in part to the fact that the pace of the game was so frenetic. That, in turn, made it a far more exciting spectacle than just about everything that has preceded it at Old Trafford this season. Yet it was strange to see the frequency with which both teams lost the ball. It was part of the fun at times but a reminder, too, of the deterioration in these teams since the days when they were authentic title challengers rather than pinning their hopes on the cups.

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The irony is that Welbeck had often looked painfully raw on his first return to Old Trafford. Di Maria could be seen early on nutmegging Alexis Sánchez then, not long afterwards, misplacing a simple pass. It was that kind of night, lots of blood and thunder but also a fair amount of thud and blunder, all at a speed that felt much more in keeping with what the home crowd at Old Trafford want to see.

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The majority will also be glad to see Rooney restored to a forward’s role, even if it felt like an awkward fit that Marouane Fellaini was dropping in just behind him. Rooney took his goal superbly, reading the flight of Di Maria’s cross and taking advantage of some generous marking to flash his header past Wojciech Szczesny. The cross was expertly delivered but Laurent Koscielny’s positioning had left Arsenal vulnerable and Rooney was left with far too much space.

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Monreal’s goal was more of a collective failure from United’s point of view, so much so that it is difficult to know who to point the finger at first. In those moments we saw Chris Smalling being sucked out to the right-back spot, Antonio Valencia becoming stranded, and Alex Oxlade-Chamberlain eluding Luke Shaw, Ashley Young and Blind before Monreal turned in the pass without anybody bothering to track his run.

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Smalling’s initial mistake had left United hopelessly dishevelled, with Mesut Özil leading the advance, and another mistake from the centre-back early in the second-half almost cost his team again. This time David de Gea held Sanchez’s deflected shot but these were moments to encourage Wenger’s side.

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Oxlade-Chamberlain had to go off with a hamstring injury around that time, whereas Shaw and Ander Herrera were both removed by Van Gaal during the interval. Phil Jones came on for Shaw and went into central defence, with Marcos Rojo moving over to the left-back position. Carrick was brought on, presumably to help provide some polish in midfield. Yet the lack of composure from United was alarming and Welbeck’s goal came from another self-inflicted wound.

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It stemmed from nothing more basic than a long goal-kick from Sczcesny. Jones took the ball down on his chest and Antonio Valencia tried to turn it back to De Gea, only to scuff the kick. Welbeck was on the ball in a flash, flicking it one side of De Gea and running round the other to score into an empty net.

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Di Maria’s final act came on 74 minutes and Arsenal could have added more but for De Gea’s goalkeeping.